1. Field of the Invention
The present invention relates to a method of producing a highly viscous, hard liquid crystal emulsion composition, in which stability of liquid crystals is improved so that the liquid crystal structure is not destroyed by dilution, with ease without applying shear force.
More specifically, the present invention relates to a method of producing a hard liquid crystal emulsion composition having an excellent stability and a viscosity 30,000 mPa·sec or more at a 2-fold dilution by using two kinds of hydrophilic surfactants having specific molecular structures with which specific components are admixed in specific mixing ratios.
2. Description of the Related Art
Conventionally, liquid crystallization using ceramides, glyceryl phospholipids, and the like has been known as in Japanese Patent Laid-open No. 124432/1997 (Patent Reference No. 1) and Japanese Patent Laid-open No. 217633/1996 (Patent Reference No. 2); however, little research has been done on liquid crystals using nonionic surfactants. Since the liquid crystal structure with the use of higher alcohols is extremely unstable and has many disadvantages, the admixing of oil components which are solid at room temperature such as paraffin and Vaseline, while reducing the admixing ratio of higher alcohols, and the use of water-soluble polymers such as gum arabic, carboxyvinyl polymers, and hydroxypropyl cellulose have been proposed to solve these disadvantages. However, the resulting products are clouded, lose transparency that is unique to liquid crystals or have increased stickiness and lack the clean texture of liquid crystals. On the other hand, Japanese Patent Laid-open No. 287718/1988 (Patent Reference No. 3) has proposed liquid crystal base materials for external application, which are composed of higher alcohols, fatty acids, hydrophilic surfactants, lipophilic surfactants, polyvalent alcohols, and water. This technique is to obtain liquid crystals by applying stirring shock using a Manton Gaulin homogenizer.
As the hydrophilic surfactants, decaglyceryl fatty acid esters, POE addition polyethylene glycol fatty acid esters, or POE addition hydrogenated castor oil have been used; however, they are not suitable for stable liquid crystal formation although they are well emulsified. As the lipophilic surfactants, fatty acid glycerides having an HLB of 7 or less have been used. The process of the production is complicated, in which oil phase components and water phase components are separately admixed and heated and the oil phase components are added to the water phase components to be pretreated using a homomixer, after which high shear force is applied by a Monton Gaulin or Manton Gaulin homogenizer. The liquid crystal structure is destroyed by dilution with water or the like to form white micelles due to the weakness of the interface membrane strength of the liquid crystals, which results in the formation of poorly stable liquid crystals.
According to Japanese Patent Laid-open No. 212716/2003 (Patent Reference No. 4), an improved liquid crystal emulsion composition composed of oil components, higher alcohols, higher fatty acids, hydrophilic surfactants, lipophilic surfactants, water-soluble polyvalent alcohols, and water has been proposed. The liquid crystals are formed by setting the amount of oily components (oil components+higher alcohols+higher fatty acids) to from 0.5 to 15.0% by weight, the ratio of the oil components to nonionic surfactants to from 1:1 to 3:1, and the number of carbon atoms of the higher alcohols to from 12 to 24 and applying stirring shock. More specifically, liquid crystals can be obtained only by a complicated process applying high shear force using a homomixer and then a Manton Gaulin homogenizer or a Microfluidizer. Further, the resulting liquid crystals are poorly stabile since the liquid crystal structure is destroyed by dilution with water or the like to change the liquid crystals from the transparent state to the state of opaque micelle emulsion.